This invention relates to alkaline electrochemical cells, typically to cells having a metal anode and an air cathode, commonly known as metal-air cells. More particularly, this invention relates to several structural features of the cell that improve the manufacturability of the cell, increase the internal volume of the cell available for active material, and improve the sealing of the cell.
Electrochemical cells are typically utilized in devices having a fixed volume available for the cell or cells. Therefore, in order to increase the volume of active material utilized in the cell, it is necessary to decrease the volume of the cell occupied by non-reactive components. Typically, this is accomplished in the field of metal-air cells by using can, cup and/or gasket components having reduced wall thicknesses.
The construction of the typical metal-air cell requires that a certain amount of volume otherwise available for active components is utilized in the creation of a step along the anode cup side wall. The step is utilized for the purpose of crimping the cell closed and is also utilized in the manufacturing process as a surface upon which force can be applied to urge the cup into a cell configuration with the cathode can and the gasket. Applicants have discovered that additional volume available for active material can be achieved by utilizing a shallow step in a metal-air cell. The shallow step increases the amount of volume available for active material while maintaining the ability to close, or crimp the cell effectively and to urge the cup into the desired position as required during the manufacturing process.
The typical metal-air cell is sealed by crimping the cathode can side walls over the step formed into the cup side wall. Applicants have discovered that a more effective seal is possible where the radius of the can crimp is greater than the radius of the cup forming the cup step. This seal is of particular advantage when used in conjunction with the shallow step of the present invention.
A shallow step creates an increased potential for the can also to nest with other cans during the manufacturing process. Either the can itself, or the assembly of the can and gasket, can tend to nest within like components as they are transported along a cell assembly line. This nesting is undesirable since the components must be separated prior to cell assembly. Applicants have discovered that this nesting can be prevented by maintaining certain internal and external diameters for the cup while still providing an enhanced volume available for active materials.
It is therefore an object of the invention to provide for an increase in the volume available for active material in an electrochemical cell such as a metal-air cell by providing a shallow step along the cup side wall.
It is further an object of the invention to provide for an improved seal for an electrochemical cell by maintaining a can crimp radius that is less than the radius defining the cup side wall step.
It is a further object of the invention to provide a cup or a cup and gasket assembly that is dimensioned such that nesting of like components is avoided.
The present invention provides an anode cup for an electrochemical cell, the anode cup comprising an upper external diameter and a lower external diameter, wherein the ratio of the upper diameter to the lower diameter is greater than or equal to about 0.86, and the ratio of the cup height at the upper diameter to the cup height at the lower diameter is not greater than about 2.19. For this minimum horizontal, or run, and maximum vertical, or rise, a shallow step is provided in accordance with the present invention.
The present invention further provides an anode cup for an electrochemical cell, the anode cup comprising a closed upper end, an open lower end and a side wall extending between the upper and lower ends, where the side wall comprises a step and a substantially vertical section between the step and the closed end. By extending the side wall vertically in the area above the step, the internal volume of a cell can be increased compared to a conventional cell, and the resultant increased volume cell advantageously fits within a conical cavity.
The present invention further provides an anode cup for an electrochemical cell where the cup comprises an upper end and a lower open end and side walls extending between the upper and lower ends, the cup having a first internal cup diameter measured at the lower open end, and an external cup diameter measured at the point where the cup corner radius blends into the cup side wall. The first internal cup diameter exceeds the external cup diameter. The cup has at least one step along the side walls, each such step defined by a first radius and a second radius along the side walls, where the first radius is toward the lower open end of the cup and the second radius is toward the upper end of the cup along the side walls. The cup has a second internal cup diameter measured at the point where the second radius blends into the cup side wall. The cup has first and second vertical heights measured from the lower end of the cup to the point where the cup corner radius blends into the side wall and to the point where the second radius of the step blends into the side wall, respectively. The external cup diameter exceeds the second internal cup diameter, and the difference of the first vertical height minus the second vertical height is greater than zero. By maintaining this relationship between the external and internal diameters of the cup, nesting of the cups is prevented during the cell assembly process in accordance with the present invention.
The present invention further provides for an anode cup and gasket assembly for an electrochemical cell. The anode cup comprises an upper end and a lower open end and a side wall extending between the upper and lower ends. The cup further comprises an external cup diameter measured at the point where the cup corner radius blends into the cup side wall. The side wall of the cup has a step formed between two substantially vertical sections. The gasket surrounds the open end of the cup, the gasket comprising an interior gasket portion disposed radially inward from the interior surface of the cup side walls and defining an inner gasket diameter. The external cup diameter exceeds the inner gasket diameter. By maintaining this relationship between the inner gasket diameter and the external diameter of the cup, nesting of the cup and gasket assembly is prevented during the cell assembly process in accordance with the present invention.
The present invention further provides for an electrochemical cell comprising an anode cup, a cathode can and a gasket disposed between the anode cup and the cathode can. The cup comprises an upper end, a lower open end and a side wall extending between the upper and lower ends. The cup further comprises at least one step along the side wall, each such step defined by a first radius and a second radius along the side wall, where the first radius is toward the lower open end of the cup and the second radius is toward the upper end of the cup along the side wall. The can comprises an upper end, a lower closed end and a side wall extending between the upper and lower can ends, the can side walls formed into a can closing radius at the shoulder area of the cell. The ratio of the total cell height to the can height is greater than 1.35. By maintaining this relationship between the total cell height and the can height, an electrochemical cell in accordance with the present invention has an increased internal volume and a more conical exterior shape compared to conventional cells. The resultant cell advantageously fits within a conical cavity and provides an increased discharge capacity, as compared to conventional cells.
The present invention further provides a button-type electrochemical cell comprising an anode cup, a cathode can and a gasket disposed between the cup and the can. The anode cup has an upper end, a lower end and side wall extending between the upper and lower ends, as well as at least one step along the side wall. Each step is defined by a first radius and a second radius along the side wall, where the first radius is toward the lower open end of the cup, and the second radius is toward the upper end of the cup along the side wall. The can has an upper end, a lower closed end and a side wall extending between the upper and lower can ends, with the can side wall formed into a cathode can closing radius at a shoulder area of the cell. A total cell height, measured from a bottom surface of said lower can end to a top surface of the upper cup end, minus a cathode can height, measured from a bottom surface of said lower can end to a top edge of said can, is greater than or equal to about 0.04 inch. The resultant cell advantageously fits within a conical cavity and provides an increased internal volume, as compared to conventional cells.
These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings.